Earnest [1] filed a deletion request for ocaml-camlp4 [2]:
This package was only necessary for a very short window when OCaml
4.02 was not yet packaged for Arch. That version stripped out camlp4
which facilitated the requirement on this one.
Since OCaml 4.02, tpowa has included community/camlp4 making this a
copy of an official package (which doesn't properly conflict due to a
difference choice of package name).
[1] https://aur.archlinux.org/account/Earnest/
[2] https://aur.archlinux.org/pkgbase/ocaml-camlp4/